Large amounts of biosolids, such as proteins, carbohydrates, fats and oils, are collected in aqueous streams during food processing operations, such as waste and wash waters from the slaughter of animals for food products and other food processing operations such as extraction of proteins during soybean processing, and the like. The aqueous stream must be clarified, i.e., have suspended solids separated and removed to recover valuable product or before being discharged from the processing plant to a municipal or public water system. When separated and dried, the biosolids have value, for example, as animal feed, crop fertilizers, in pharmaceuticals and in personal care products. In one particular example, recovered protein from soybeans may be used in infant formula.
These biosolids are comprised of particles having surface charges. Typically the particles have anionic surface charges at alkaline and neutral pH. The surface charge generates a repulsive force between particles to keep them apart. For individual particles of colloidal size, such as proteins, gravitational
forces are insufficient to cause them to settle out of the aqueous suspension. Simple separation methods, such as filtration, are ineffective to separate these protein solids due to blinding of filters or ability of the solids to pass through them. Thus separation and hence, recovery of the protein may be low and/or a waste stream may not be environmentally acceptable for discharge from the processing plant.
Techniques for removal of proteins, carbohydrates, fats and oils, and other biological contaminants from aqueous food processing streams are known. A common practice is to separate the protein, fats and oils from the aqueous stream by flocculation with metal salts, especially iron and/or aluminum salts, and anionic polymers. As it is common to use the recovered proteins, carbohydrates, fats and oils in animal feed, there are health issues when metal salts are used to separate biosolids. There is concern that the recovered biosolids have high levels of metal salts, which may build up in the tissues of the animals to whom the feed is given, these tissues being subsequently consumed by humans. Animal nutritionists are also concerned that metal salts may bind to phosphates in the feed so that they are less available as a nutrient. The food processing industry has sought alternatives to the use of metal salts for separation of proteins, carbohydrates, fats, and oils from aqueous streams.
While methods have been disclosed for clarification of aqueous streams from food processing plants and separation of biosolids therefrom which do not require metal salts, each of these suffer from disadvantages such as high costs of materials and long period to sufficiently clarify the stream. The present invention provides an economic and efficient process to clarify aqueous streams from food processing and to separate and recover protein in a form capable of subsequent commercial use.